1. Field of the Invention
The present invention relates to an optical device, and more particularly to an optical fiber block utilized as an optical connector.
2. Description of the Related Art
An optical fiber block is typically used as an input or output terminal of micro-optic devices and further used in aligning and connecting an optical fiber or optical fiber array with input or output terminals of a planar lightwave circuit (PLC).
FIG. 1 is a schematic diagram showing the construction of a conventional arrayed waveguide grating module, and FIG. 2 is a perspective view of a single-core optical fiber block employed in the arrayed waveguide grating module shown in FIG. 1. FIG. 3 is a sectional view of the single-core optical fiber block shown in FIG. 2, taken along line A—A. FIG. 4 is a perspective view of a multi-core optical fiber block employed in the arrayed waveguide grating module shown in FIG. 1, and FIG. 5 is a sectional view of the multi-core optical fiber block shown in FIG. 4, taken along line B—B.
Referring to FIG. 1, the arrayed waveguide grating module according to the prior art includes a single-core optical fiber block 110, an arrayed waveguide grating 130, and a multi-core optical fiber block 150.
Referring to FIG. 2, the single-core optical fiber block 110 includes a first optical fiber 112, a first substrate 118, and a first flat glass plate 120. The first optical fiber 112 includes a bare optical fiber 114 and its coating layer 116. A portion of the bare optical fiber 114 with a predetermined length from one end of the first optical fiber 112 is not covered by the coating layer 116.
Referring to FIG. 3, the first substrate 118 has a V-shaped groove 119 formed on the upper surface of the first substrate 118, and the bare optical fiber 114 is seated in the V-shaped groove 119. After the bare optical fiber 114 is seated in the V-shaped groove 119, epoxy is applied on the first substrate 118 and the first optical fiber 112 to fix the first optical fiber 112. Then, the first flat glass plate 120 is placed on the epoxy applied on the first substrate 118 and the first optical fiber 112, thereby fixing the first optical fiber 112 and protecting the first optical fiber 112 from the external environment.
Referring back to FIG. 1, the arrayed waveguide grating 130 is a planar waveguide device, which includes an input optical waveguide 132, a first slab waveguide 134, an array of grating waveguides 136, a second slab waveguide 138, and an array of output optical waveguides 140. One end of the input optical waveguide 132 is connected with the first optical fiber 112, and the other end of the input optical waveguide 132 is connected with the first slab waveguide 134. The first slab waveguide 134 distributes an optical signal inputted through the input optical waveguide 132 to the arrayed grating waveguides 136. The arrayed grating waveguides 136 includes a plurality of optical waveguides having different lengths, wherein one end of each of the arrayed grating waveguides 136 is connected with the first slab waveguide 134 while the other end is connected with the second slab waveguide 138. The second slab waveguide 138 distributes the optical signal inputted through the arrayed grating waveguides 136 to the arrayed output optical waveguides 140 according to their wavelengths.
The arrayed output optical waveguides 140 include a plurality of optical waveguides, each of which has one end connected with the second slab waveguide 138 and the other end connected with the multi-core optical fiber block 150. The multi-core optical fiber block 150 includes an array of second optical fibers 152, a second substrate 158, and a second flat glass plate 160. The arrayed second optical fibers 152 include bare optical fibers 154 and coating 156. A portion of each bare optical fiber 154 with a predetermined length from one end of a corresponding second optical fiber 152 is exposed without the coating 156.
Referring to FIG. 4, the second substrate 158 has V-shaped grooves 159 formed on its upper surface, spaced at predetermined intervals apart from each other, and the bare optical fibers 154 are seated in the V-shaped grooves 159 one by one. After the bare optical fibers 154 are seated in the V-shaped grooves 159, epoxy is applied on the second substrate 158 and the second optical fibers 152 to fix the second optical fibers 152. Thereafter, the second flat glass plate 160 is placed on the epoxy applied on the second substrate 158 and the second optical fibers 152, thereby fixing the second optical fibers 152 and protecting the second optical fibers 152 from the external environment.
In the arrayed waveguide grating module described above, it is important for each of the output optical waveguides 140 of the arrayed waveguide grating 130 to keep a constant output wavelength and output power, and the wavelength of each output optical waveguide 140 must satisfy a wavelength standard recommended by the International Telecommunication Union (ITU) within an operation temperature range. That is, the gap between the output wavelengths must be a value within ±0.04 nm in the case where the output wavelengths have a frequency of 100 GHz. Further, it is preferable that the gap between the output wavelengths is ±0.01 nm smaller than the above limit, due to a wavelength error generated when the arrayed waveguide grating 130 is manufactured. In this case, the operation temperature range, which varies according to the module, is between −5° C. and 65° C. in the case of a heater-type module, which has the broadest operation temperature range.
As described above, when the operation temperature changes in the arrayed waveguide grating module, the wavelength of the optical signal outputted through each output optical waveguide 140 changes slightly. This change of wavelength deteriorates the performance of the arrayed waveguide grating module. In other words, as the arrayed waveguide grating 130 is made of silicon or silica, the refractive index of the arrayed waveguide grating 130 changes depending on the temperature, thereby generating the above-mentioned change in the wavelength.
The thermal change Θ defined by Expression 1 below must be compensated for.                     Θ        =                              ⅆ            λ                                ⅆ            T                                              [                  Expression          ⁢                                           ⁢          1                ]            
Further, a predetermined compensation factor αL (α represents the difference between thermal expansive coefficients of the arrayed waveguide grating and the optical fiber block, and L represents a predetermined distance) must be considered in manufacturing the arrayed waveguide grating module.
As described above, the conventional arrayed waveguide grating module requires a compensation for temperature change. Moreover, in the case of a heater-type arrayed waveguide grating module, the lifespan of the module is shortened, and the module must be provided with an additional electric circuit for maintaining a desired temperature.